Bacterial contamination of platelet concentrates represents a risk of morbidity and mortality in transfusions. Approximately 1 in 2000 to 1 in 5000 platelet concentrates are believed to be bacterially contaminated. In 2004, the Food and Drug Administration (FDA) recommended bacterial testing of all platelet units. The American Association of Blood Banks (AABB) standard 5.1.5.1 requires bacterial testing on every platelet unit (thus requiring 100% quality control). Canada produces approximately 300,000 platelet concentrates annually. In the United States, about 4 million platelet products are produced every year. Even testing of pooled products means millions of tests annually in North America alone. Furthermore, the current proposal in the industry to extend platelet storage from 5 to 7 days will require bacterial testing.
Currently, platelet concentrate units are only tested for bacteria at the end of the manufacturing process (i.e. at Day 0 or Day 1 of storage). This single test involves sampling of 4-10 ml from the platelet unit into a growth bottle. After 24-48 hours of culture, aerobic bacteria are measured by the amount of CO2 production. Facultative/anaerobic bacteria are measured by the amount of O2 production. Two different culture bottles are required for the two different metabolites. The only approved instrument known to Applicant is the BacT/ALERT® from bioMérieux (http://www.biomerieux-usa.com). However, one shortcoming of using this instrument is that the platelet product cannot be released for 1-2 days until the BacT/ALERT® results are available. Because of the sampling requirement, this is a one-time test. As contamination levels are usually low at the beginning, the BacT/ALERT® yields a high rate of false-negative results. In other words, samples that are thought to be bacteria-free may actually turn out later to be contaminated because the BacT/ALERT® lacks the sensitivity to detect low levels of bacteria in the sample at an early stage.
In view of the shortcomings of the prior art, an improved method for detecting bacterial contamination in a sample remains highly desirable.